Method and apparatus for performing turbo decoding based on channel information

ABSTRACT

A method and an apparatus for carrying out a turbo decoding by utilizing the channel information are disclosed. When using a turbo-decoder in a wireless communication system, in order to reduce the decoding delay, the channels are estimated by using the information such as a pilot channel information or a pilot symbol information, and the number of iterative decoding is controlled by utilizing the signal-to-interference ratio (SIR), thereby shortening the decoding delay, and making the quality of the high speed multi-media service better and reliable. The turbo code decoding apparatus utilizing a channel information according to the present invention includes a channel estimator for estimating a channel status based on reception signals to measure a SIR. Further, an iterative decoding times controller controls the number of iterative decoding by comparing the SIR with a pre-set threshold value. Further, a decoder carries out the iterative decoding as many times as controlled by the iterative decoding times controller. The present invention is applied to communication systems.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and an apparatus forperforming an iterative decoding of turbo code; and, more particularly,to a method and an apparatus for controlling the number of iterativedecoding of turbo code based on channel information, which reducedecoding delay and maintain the required quality of service in awireless communication system, and a recording medium for achieving themethod and apparatus.

DESCRIPTION OF THE PRIOR ART

[0002] Generally, in the wireless communication field such as mobilecommunication, significant loss is occurred due to the wireless channelimpairments such as propagation path loss, multi-path components andshadowing effect. The impairments cause random errors and burst errors.

[0003] In order to correct the errors such as random errors and bursterrors, error correction codes are used as a method of improving thereliability.

[0004] Recently many studies are continued for applying the turbo codeto the 3rd generation mobile communication (IMT-2000). The turbo code isknown to have powerful performance compared with the convolutional code.The convolutional code is being currently used in the mobilecommunication system.

[0005] The turbo code is constituted such that the RSC (recursivesystematic convolutional) codes are connected in parallel, so as to makeit possible to decode through iterative decoding (which is a sub-optimaldecoding method).

[0006] Further, the turbo code shows an excellent performance whichapproaches to the Shannon limit in case of the interleaver having alarge size and sufficient iterative decoding in AWGN channel.

[0007]FIG. 1 shows the constitution of a turbo decoding scheme.

[0008] As shown in this drawing, the encoding apparatus includes: aninterleaver 111˜11(n−1) for reducing the correlations by interleavingthe input transmission information bits; an encoder 121 for encoding theinput transmission information bits; encoders 122˜12n for encoding theinterleaved signals through relevant interleavers 111˜11(n−1); and amultiplexer 130 for selectively transmitting the encoded parity bits andinformation bits after encoding by the encoders 121˜12n.

[0009] As shown in the drawing, the transmission information bits may betransmitted without being encoded, or may be transmitted after beingencoded by the encoders 121˜12n into parity bits.

[0010] The encoded parity bits and information bits are selectivelytransmitted by the multiplexer 130, and therefore, it is possible tochange the code rate from 1 to 1/n.

[0011] Further, in the wireless communication system, if the abovedescribed apparatus is used, its performance depends on the number ofiteration. If a high quality of service (QoS) is required under severfading channel, the number of iteration has to be increased in order tomeet QoS requirement.

[0012] However, if additional information on the channels is notavailable for controlling the number of iteration, the decoding iscarried out at the fixed number of iteration.

[0013] Under this condition, if the status of the wireless communicationchannels has been severely degraded, the fixed number of iteration isinsufficient and the degradation of the performance cannot be avoided.On the other hand, if the channel environment is good and thesignal-to-interference ratio (SIR) is high the fixed large number ofiteration results in decoding delay.

SUMMARY OF THE INVENTION

[0014] The present invention is intended to overcome the above describeddisadvantages of the conventional technique which is based on the fixednumber of iteration.

[0015] Therefore, it is an object of the present invention to provide amethod and an apparatus for carrying out a turbo decoding, and arecording medium for achieving the method and apparatus in order toreduce the decoding delay in a high SIR and maintain the requiredquality of service in a low SIR. The SIR is measured by the givenchannel information such as pilot channel or pilot symbol.

[0016] In order to reduce the decoding delay in a high SIR and maintainthe required quality of service in a low SIR, the number of iteration iscontrolled based on the SIR, thereby shortening the decoding delay, andmaking the quality of the high speed multi-media service better andreliable.

[0017] To achieve the above object, in accordance with an aspect of thepresent invention, the turbo code decoding apparatus utilizing channelinformation according to the present invention includes: a channelestimator for estimating a channel status based on asignal-to-interference ratio (SIR); an iterative decoding controller forcontrolling the number of iterative decoding by comparing the SIR with apre-set threshold value; and a decoder for carrying out iterativedecoding as many times as controlled by the number of iterativedecoding.

[0018] In accordance with another aspect of the present invention, theturbo code decoding apparatus utilizing a channel information accordingto the present invention includes: a channel estimator for estimating achannel status based on a signal-to-interference ratio (SIR); a powercontrol bit generator for generating transmission power control (TPC)bits correspondingly with the SIR of the channel estimation means; aniterative decoding times controller for controlling the number ofiterative decoding in accordance with the power control bits of thepower control bit generating means; and a decoder for carrying outiterative decoding as many times as controlled by the number ofiterative decoding.

[0019] In accordance with still another aspect of the present invention,the turbo code decoding method utilizing channel information by using aturbo code decoding apparatus according to the present inventionincludes the steps of: measuring a signal-to-interference ratio (SIR) byestimating a channel status based on reception signals; deciding thenumber of iterative decoding by comparing the SIR with a pre-setthreshold value; and carrying out iterative decoding as many times ashas been decided.

[0020] In accordance with still another aspect of the present invention,the turbo code decoding method utilizing channel information by using aturbo code decoding apparatus according to the present inventionincludes the steps of: measuring a signal-to-interference ratio (SIR) byestimating a channel status based on reception signals; generatingtransmission power control (TPC) bits correspondingly with the SIRmeasured; deciding the number of iterative decoding in accordance withthe power control bits thus generated; and carrying out the iterativedecoding as many times as has been decided.

[0021] In accordance with still another aspect of the present invention,there is provided a computer readable recoding media storinginstructions for executing a method for performing a turbo decodingbased on channel information, the method comprising the steps of: a)measuring a signal-to-interference ratio (SIR) by estimating a channelstatus based on reception signals; b) deciding the number of iterativedecoding by comparing the SIR with a pre-set threshold value; and c)carrying out iterative decoding as many times as has been decided.

[0022] In accordance with still another aspect of the present invention,there is provided a computer readable recoding media storinginstructions for executing a method for performing a turbo decodingbased on channel information, the method comprising the steps of: a)measuring a signal-to-interference ratio (SIR) by estimating a channelstatus based on reception signals; b) generating transmission powercontrol (TPC) bits correspondingly with the SIR measured; c) decidingthe number of iterative decoding in accordance with the power controlbits thus generated; and d) carrying out the iterative decoding as manytimes as has been decided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above objects and other advantages of the present inventionwill become more apparent by describing in detail the preferredembodiment of the present invention with reference to the attacheddrawings in which:

[0024]FIG. 1 is a block diagram showing the constitution of a turboencoding apparatus;

[0025]FIG. 2 is a block diagram showing the constitution of the turbodecoding apparatus utilizing the channel information according to thepresent invention;

[0026]FIG. 3 is a flow chart showing the constitution of the turbodecoding method utilizing the channel information according to thepresent invention;

[0027]FIG. 4 is a block diagram showing the constitution of anotherembodiment of the turbo decoding apparatus utilizing the channelinformation according to the present invention; and

[0028]FIG. 5 is a flow chart showing the constitution of anotherembodiment of the turbo decoding method utilizing the channelinformation according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The preferred embodiments of the present invention will bedescribed in detail referring to the attached drawings.

[0030]FIG. 2 is a block diagram showing the constitution of the turbodecoding apparatus utilizing the channel information according to thepresent invention. The signal-to-interference ratio (SIR) which has beenestimated by utilizing channel information is compared with a pre-setthreshold value so as to control the number of iterative decoding.

[0031] As shown in FIG. 2, the turbo decoding apparatus utilizing thechannel information according to the present invention includes: channelestimators 210 and 211 for measuring the SIR by estimating the wirelesschannel status based on the received pilot channel signals or thereceived pilot symbol signals; a comparator 220 for comparing the SIRmeasured by the channel estimators 210 and 211 with a pre-set thresholdvalue so as to output a control information on the number of iterativedecoding; an iterative decoding control counter 230 for counting up anddown the number of iterative decoding in accordance with the outputvalue of the comparator; a switch 240 for controlling iterative decodingin accordance with the number of iterative decoding of the counter 230;and a decoding part 250 for carrying out the iterative decoding as manytimes as controlled by the counter 230.

[0032] The decoding part 250 includes: an MAP1 (Maximum A Posteriori 1)decoder 251; an interleaver 252; an MAP2 (Maximum A Posteriori 2)decoder 253; and deinterleavers 254 and 255.

[0033] This is a known technology, and therefore, it will not bedescribed more here.

[0034] The turbo decoding apparatus of the present invention which isconstituted as above will now be described as to its operations.

[0035]FIG. 3 is a flow chart showing the constitution of the turbodecoding method utilizing the channel information according to thepresent invention. Here, the SIR is applied to control the number ofiterative decoding.

[0036] First, parameters are set up for controlling the number ofiterative decoding for the turbo code at step 300. The parametersinclude the maximum number of iteration (Nmax), the minimum number ofiteration (Nmin) and the threshold of the comparator, which aredetermined according to the required quality of service and the limiteddecoding delay.

[0037] Then in order to decide the number of iterative decoding, thechannels are estimated using the channel estimators 210 and 211. The SIRis measured at step 301.

[0038] Then the measured signal-to-interference ratio is compared with apre-set threshold value at step 302, and if the measured SIR is largerthan the threshold value, the value N of a counter which counts thenumber of iterative decoding is decreased at step 303. On the otherhand, if the measured SIR is smaller than the threshold value, it meansthe severe wireless channel environment, and therefore, the value N ofthe counter is increased at step 304 so as to maintain the requiredperformance.

[0039] Then, a comparison is carried out to know as to whether the valueof counter N lies in the Nmax˜Nmin range (e.g., 2˜20) for satisfying theminimum performance requisite, thereby carrying out a confirmation.

[0040] That is, at step 305, it is determined whether the adjustedcounter value N is larger or smaller than the maximum number Nmax ofiteration or the number of minimum number of iteration Nmin. If N islarger than Nmax, then N is fixed to Nmax at step 306, while if N issmaller than Nmax, then N is compared with Nmin to maintain the minimumperformance level at step 307.

[0041] If N is found to be smaller than Nmin as a result of thecomparison, then N is set to Nmin at step 308, while if N lies betweenNmin and Nmax, N is fixed without variation.

[0042] When the value of N is decided through the above describedprocedure, the code words which have been encoded by the encoders 1 and2 of FIG. 1 at the transmitting end (with the code rate of ⅓) aredecoded by MAP1 and MAP2 at steps 309 and 310.

[0043] Under this condition, the decoding is carried out as many timesas the value N of the counter.

[0044] Each time when an iterative decoding is carried out, the value ofthe counter is diminished by 1 at step 312. Thus the value N is checkedat step 311, and when N becomes 0, the decoding is terminated, therebyobtaining a decoded final data.

[0045] The above described procedure is carried out for each slot, orfor an integer-multiple of the basic slot, or for each frame.

[0046]FIG. 4 is a block diagram showing the constitution of anotherembodiment of the decoding apparatus utilizing the channel informationaccording to the present invention. Here, power control bits aregenerated correspondingly with the SIR which is obtained by utilizingthe channel information, thereby controlling the number of iterativedecoding.

[0047] As shown in FIG. 4, the turbo decoding apparatus based on thechannel information according to the present invention includes: channelestimators 410 and 411 for measuring the SIR by estimating the channelstatus of the pilot channel signals or the pilot symbol signals; atransmission power control bit generator 420 for generating thetransmission power control bits (TPC) correspondingly with the SIR ofthe channel estimators 410 and 411; an iterative decoding controlcounter 430 for counting the number of iterative decoding in accordancewith the transmission power control bit generator 420 to output acontrol information on the number of iterative decoding; a switch 440for controlling the number of iterative decoding in accordance with thevalue of counter 430; and a decoding part 450 for carrying out iterativedecoding as many times as controlled by the switch.

[0048] The decoding part 450 includes: an MAP1 (Maximum A Posteriori 1)decoder 451; an interleaver 452; an MAP2 (Maximum A Posteriori 2)decoder 453; and deinterleavers 454 and 455.

[0049] This is a known technology, and therefore, it will not bedescribed any more here.

[0050] The turbo decoding apparatus of the present invention which isconstituted as above will now be described as to its operations byreferring to FIG. 5.

[0051]FIG. 5 is a flow chart showing the constitution of anotherembodiment of the turbo decoding method utilizing the channelinformation according to the present invention. Here, power control bitsare generated to control the number of iterative decoding for turbo codehaving a code rate of ⅓.

[0052] First, parameters are set up for controlling the number ofiterative decoding for the turbo code at step 501.

[0053] The parameters include the maximum number of iteration (Nmax),the minimum number of iteration (Nmin) and the threshold of thecomparator, which are determined according to the required quality ofservice and the limited decoding delay.

[0054] Then, in order to control the number of iterative decoding, thepilot channel information or the pilot symbol information is utilized toestimate the channel so as to obtain the SIR at step 502. Then TPC(transmission power control) bits are generated correspondingly with themeasured SIR at step 503.

[0055] Then a checking is carried out as to whether a power decreasecommand is inputted from the terminal to the base station or from thebase station to the terminal at step 504.

[0056] Upon the checking, if it is found that a power increase commandhas been inputted from the terminal to the base station or from the basestation to the terminal, then a closed loop power control is carriedout, and the number of iterative decoding of the turbo decoder isincreased in accordance with the power increase command at step 506.

[0057] Upon the checking, on the contrary, if it is found that a powerdecrease command has been inputted, then the number of iterativedecoding is decreased at step 505.

[0058] The value of N which has been decided by the power control bitsis subjected to a checking as to whether the minimum service qualityrequisite (value of Nmin) and the delay limitation (value of Nmax) issatisfied at steps 507 to 510.

[0059] That is, the adjusted value N of the counter is compared with themaximum repetition value Nmax at step 507, and if N is larger than Nmax,then N is fixed to Nmax at step 508. On the other hand, if N is smallerthan Nmax, N is compared with Nmin which is the minimum repetition timesat step 509.

[0060] Upon comparing N with Nmin, if it is found that N is smaller thanNmin, then N is set to Nmin at step 510, while if N lies between Nminand Nmax, then N is kept as it is.

[0061] When N is decided through the above described procedure, the codewords which have been encoded at the transmission end of FIG. 1 by theencoders 1 and 2 having a code rate of ⅓ are decoded by MAP1 and MAP2 atsteps 511 and 512. Under this condition, the decoding is carried out asmany times as N which has been decided through the above describedprocedure.

[0062] Each time when an iterative decoding is carried out, the countervalue is diminished by 1 at step 514, and checking is carried out on thevalue of N. Ultimately, when the value of N becomes zero, the decodingis terminated, thereby obtaining the finally decoded data.

[0063] The above described procedure is carried out for each slot, orfor an integer-multiple of the basic slot, or for each frame.

[0064] Meanwhile, the method of estimating the optimum channel can bedifferent depending on the pilot structure which is used. However, inthe general pilot channels and the general pilot symbols, the estimationcan be carried out by utilizing a moving average filter.

[0065] According to the present invention as described above, thechannel information which is given in the wireless communication systemis utilized so as to efficiently control the number of iterativedecoding for the turbo code. Thus the problem of the decoding delay canbe solved in a high SIR by reducing the number of iteration keeping therequired performance and also it is possible to afford a requiredquality service in a low SIR by increasing the number of iterationwithin the range of iteration (Nmin˜Nmax).

[0066] Further, as the decoding delay time is shortened, the powerconsumption can be saved, and therefore, the overall capacity of thesystem can be expanded.

[0067] Although the preferred embodiments of the present invention havebeen disclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. An apparatus for performing a turbo decoding based on channel information, comprising: a channel estimation means for estimating a channel status based on reception signals to measure a signal-to-interference ratio (SIR); an iterative decoding times control means for controlling a number of iterative decoding by comparing the SIR with a pre-set threshold value; and a decoding means for carrying out iterative decoding as many times as controlled by said iterative decoding times control means.
 2. The apparatus as recited in claim 1, wherein said iterative decoding times control means includes: an iterative decoding times deciding means for comparing the SIR of said channel estimation means with a threshold value to increase or decrease the number of iterative decoding, and for comparing the iterative decoding times with the minimum number of iteration and the maximum number of iteration to decide the iterative decoding times.
 3. An apparatus for performing a turbo decoding based on channel information, comprising: a channel estimation means for estimating a channel status based on reception signals to measure a signal-to-interference ratio (SIR); a power control bit generating means for generating transmission power control (TPC) bits correspondingly with the SIR of said channel estimation means; an iterative decoding times control means for controlling a number of iterative decoding in accordance with the power control bits of said power control bit generating means; and a decoding means for carrying out the iterative decoding as many times as controlled by said iterative decoding times control means.
 4. The apparatus as recited in claim 3, wherein said iterative decoding times control means includes: an iterative decoding times deciding means for increasing/decreasing the number of iterative decoding in accordance with power increase/decrease commands based on the power control bits of said power control bit generating means to increase/decrease the number of iterative decoding, and for comparing the number of iterative decoding with the minimum number of iteration and the maximum number of iteration to decide the number of iterative decoding.
 5. A method for performing a turbo decoding based on channel information, comprising the steps of: a) measuring a signal-to-interference ratio (SIR) by estimating a channel status based on reception signals; b) deciding a number of iterative decoding by comparing the SIR with a pre-set threshold value; and c) carrying out iterative decoding as many times as has been decided.
 6. The method as recited in claim 5, wherein the step b) includes the steps of: b1) comparing the SIR with the pre-set threshold value to increase/decrease the number of iterative decoding; and b2) comparing the increased/decreased number of iterative decoding with the minimum number of iteration and the maximum number of iteration to decide the number of iterative decoding.
 7. A method for performing a turbo decoding based on channel information, comprising the steps of: a) measuring a signal interference ratio (SIR) by estimating a channel status based on reception signals; b) generating transmission power control bits (TPC) correspondingly with the SIR measured; c) deciding a number of iterative decoding in accordance with the power control bits thus generated; and d) carrying out the iterative decoding as many times as has been decided.
 8. The method as recited in claim 7, wherein the step c) includes the steps of: c1) increasing/decreasing the number of iterative decoding in accordance with a power increase/decrease command based on values of the power control bits; and c2) comparing the number of the increased/decreased iterative decoding with the minimum number of iteration and the maximum number of iteration to decide the number of iterative decoding.
 9. A computer readable recoding media storing instructions for executing a method for performing a turbo decoding based on channel information, the method comprising the steps of: a) measuring a signal-to-interference ratio (SIR) by estimating a channel status based on reception signals; b) deciding a number of iterative decoding by comparing the SIR with a pre-set threshold value; and c) carrying out iterative decoding as many times as has been decided.
 10. A computer readable recoding media storing instructions for executing a method for performing a turbo decoding based on channel information, the method comprising the steps of: a) measuring a signal-to-interference ratio (SIR) by estimating a channel status based on reception signals; b) generating transmission power control bits (TPC) correspondingly with the SIR measured; c) deciding a number of iterative decoding in accordance with the power control bits thus generated; and d) carrying out the iterative decoding as many times as has been decided. 